Active Mind, Body Linked to Brain Growth

Regular running and intensive mental exercise may revitalize the mind by spurring the growth of new brain cells responsible for learning and memory, new animal experiments suggest.

The research, made public Monday, sheds light on how the effects of daily experience can foster new brain cells in adult mammals from mice to human beings. In essence, the research suggests that an active life--whether the activity be physical or mental--can have a positive impact on the brain.

In separate studies published in Nature Neuroscience, scientists at the Salk Institute for Biological Studies in La Jolla and at Princeton University discovered that some kinds of physical and mental exercise promoted the growth of new neurons, while also measurably prolonging the survival of existing brain cells. The changes took place in a part of the brain called the hippocampus, which is crucial to the formation of new memories.

"That is terribly exciting, given that we know the hippocampus plays a role in the memory of new facts and new events," said Neal J. Cohen, a cognitive neuroscientist at the University of Illinois. "It is clear the adult brain continues to be modified structurally and functionally by experience."

The Salk researchers, to their surprise, found that adult mice exercising on a running wheel regularly developed twice as many new brain cells in the hippocampus as mice housed in standard cages.

The scientists had designed their experiment to test the effects of learning and had only included the running wheels as one of several different variables. The mice ran at their own pace, as often and for as long as they liked.

"The difference was so striking," said neurobiologist Fred H. Gage, senior author of the Salk study. "And because we know now that human brains also make new cells, it just might be that running or other vigorous exercise stimulates brain cell production in people as well."

Until recently, the idea that the human brain can produce new neurons well into old age was a scientific heresy. Most experts were convinced the human brain had done almost all its growing by the time a child was born.

But several animal studies have shown that, contrary to expectations, the hippocampus of the adult brain can produce thousands of new neurons every day. Recently, Gage and his colleagues demonstrated that the human brain is no exception, producing new neurons even in the elderly.

The Salk researchers do not know why running should have such an enhancing effect on neural development. Running might increase the flow of oxygen and nutrients to brain tissues or release special growth factors that promote new neurons, Gage said.

It may well be that the primordial biology of running prompts the nervous system to prepare for an onslaught of new information as an animal navigates unfamiliar terrain in the pursuit of prey or in flight from an enemy. In those situations, the brain may respond reflexively to running by expanding its store of neurons in anticipation of new learning, several experts said.

"Exercise itself over the eons may have become associated with a bunch of effects that help the brain prepare itself for new information, new learning, new brain work," Cohen at Illinois said.

In their experiments, the Princeton team found that purely mental tasks could double the number of new neurons in the adult hippocampus and help existing neurons live longer.

Mental challenges that required the animals to master information involving spatial relationships and timing, which placed special demands on the hippocampus, had the greatest effect. The lab mice, for example, had to learn how to locate platforms in a water maze, which tested their ability to put together spatial relationships. Learning tasks that did not place demands on the hippocampus had no effect.

"It is a classic case of 'use it or lose it,' " said Princeton psychologist Elizabeth Gould, who conducted the research. "Certain types of learning that require this brain region--the hippocampus--were very good at rescuing new neurons from death. It was not just learning in general. It was not experience in general."

Although the Princeton research was not intended to address human well-being directly, the animal experiments underscore the importance of an active life of the mind, Gould said.

"It is very likely if you lead a very mentally active life you are engaging the hippocampus," Gould said.

If the right kind of mental exercise promotes a healthy mind, the absence of mental stimulation may have an equally harmful effect on the brain, by allowing neurons to atrophy and die. "A lack of learning opportunities may have a negative structural impact on the brain," Gould said.

Together, the findings hint at the physical mechanisms underlying the human brain's unexpected "flexibility," its ability to change in response to experience.

Previous studies have shown that animals, including primates, created more new cells in the hippocampus if they lived in a more stimulating, enriched environment rather than in a standard cage. In the new research, the two teams of scientists were trying to pinpoint the tasks most likely to spur new brain cells.

"I think it is a pretty big deal," said neuroscientist Janice Juraska at the University of Illinois, who studies brain development. "It helps explain why we are as flexible as we are."

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Exercising the Brain's Gray Matter

New research with laboratory animals suggests that running regularly might build up the number of neurons in an area of the brain called the hippocampus, while other new research shows that learning can help brain cells there live longer.